598 FUNCTIONS OF THE CEREBRO-SPINAL NERVOUS SYSTEM. 



magnum to the first or second lumbar vertebra, and which is prolonged as 

 the filum terminate 1 to the extremity of the sacral canal, is almost com- 

 pletely divided by the anterior and posterior median fissures (Fig. 207, a, p\ 

 into two lateral and symmetrical halves. The " anterior median fissure " 

 (a) is more distinct than the posterior, being wider at the surface; but it 

 only penetrates to about one-third of the thickness of the Cord, its depth 

 increasing, however, towards its lower part. The sides of the " posterior 

 median fissure" (p), on the other hand, are in closer approximation; but 

 the division commonly extends to about half the thickness of the cord, being 

 deeper towards its upper than towards its lower end. The two halves, there- 

 fore, are only united by a commissural band, which occupies the central part 

 of the cord ; and this is traversed by the " Spinal canal " (/), which is con- 

 tinued downwards from the fourth ventricle, is about y-J-gth of an inch in 



FIG. 207. 



' 



Transverse section of Spinal Cord,- through the middle of the lumbar enlargement, showing on the 

 right side the course of the nerve-roots, and on the left the position of the principal tracts of vesicular 

 matter: A, A, anterior columns; p, p, posterior columns; L, L. lateral columns; a, anterior median fis- 

 sure ; p, posterior median fissure; l>, b, b, b, anterior roots of spinal nerves; c,<\ posterior roots; d, d, 

 tracts of vesicular matter in anterior column ; e, tracts of vesicular matter in posterior column, termed 

 hy Jacubowitsc.h the " sympathetic " column or tract ;/, central canal, surrounded by the gray com- 

 missure ; g, substautia gelatinosa of Rolando. 



diameter, and according to Mr. Lockhart Clarke, is lined with a layer of 

 columnar ciliated cells, whose attached extremities taper into delicate fibres, 

 becoming continuous with the fibres of the connective tissue of the white 

 columns. At a little distance from either side of the posterior median fis- 

 sure, and corresponding with the line of attachment of the posterior roots 

 of the nerves, is the posterior lateral furrow ; a shallow, longitudinal depres- 

 sion, which marks out the "posterior columns" of the Cord (p, P) as dis- 

 tinct from the " antero-lateral columns." A corresponding furrow has been 

 sometimes described as traversing the Cord in the line of the anterior roots 



1 The structure of the "filum terminalc" is in every respect essentially the same 

 as that of the proper Spinal Cord, save that no nerve-roots are connected with it. 



